Fig. 1.
The first illustration I shall show you from Hero’s work is a bird which, by means of a stream of water, is caused to pipe or sing. This little automaton consists of a pedestal (A B C D) ([Fig. 1]), which is in reality a water-tight tank fitted with a funnel (E), the stem of which reaches nearly to the bottom; to the right of this there is a little bush on which sits a bird, and a tube (G H) leads up from the roof of the tank and terminates in a little whistle, the end of which dips into a cup (L) containing water. When water is poured into the funnel, the air in the tank is driven out through the tube and whistle (G H) and, bubbling through the water, sounds as if the bird were singing. Thus the well-known bubbling bird-whistle dates back to a century and a half before the Christian era or earlier.
The next illustration ([Fig. 2]) shows a more elaborate arrangement, in which there are four small birds being watched by an owl; the moment the owl’s back is turned the birds begin to sing, but cease as soon as he turns towards them. In this apparatus the birds are made to sing in precisely the same way as in the last illustration, namely, by the displacement by water of the air in the tank, but as soon as the level of the water in the tank reaches the top of a concentric siphon (F G) the water is discharged into a bucket, the birds cease to sing, and the bucket, owing to its increased weight, lifts the counterbalance weight (Z), and in doing so turns the spindle (P M) which supports the owl (R S). When the bucket is full its contents are discharged by a small siphon within it and it is drawn up by the weight (Z) the owl turns its back to the birds, and the cycle of operations is repeated.
Fig. 2.
In the next figure a still more elaborate effect is produced. Here is a pedestal upon which are four little bushes each having a bird sitting in its branches; when water is allowed to flow into the funnel the first bird begins to whistle, and after a few minutes leaves off, when the next bird begins, and when he has finished the third bird sings, after a little time the fourth takes up the song, and when he has finished the first begins again, and so on as long as water is flowing into the funnel. These effects are produced in the simplest possible manner, by a combination of as many superposed tanks as there are birds to sing, the one emptying into the other by siphons. The illustration explains itself.
Fig. 3.